A shield room configuring a shield apparatus effectively shields a high-frequency magnetic field, as well as a direct current (DC) low-frequency magnetic field, based on both a magnetic field shield effect obtained using a soft magnetic material of high permeability and an eddy current shield effect obtained using a metal of high electrical conductivity. Such a shield room is generally manufactured in double or triple walls in order to enhance shield effectiveness, and each of the walls is formed in dual layers of a soft magnetic layer and a high-conductivity metal layer.
FIG. 1 is a perspective view showing a shield apparatus 1 provided with a shield room 2 having multiple walls according to a prior art, and FIG. 2 is a cross-sectional view showing a shield apparatus 1 provided with a shield room 2 having multiple walls according to a prior art. That is, FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1. As shown in FIGS. 1 and 2, the shield room 2 having multiple walls of the prior art uses a magnetic material such as Mu-metal, permalloy or the like containing nickel as a material having high permeability for all inner layers regardless of magnetic field strength in a space. Then, the distance between the walls is about 10 to 30 cm, and a metal layer 4 formed of aluminum having high conductivity is installed as an outer layer of each wall.
In the shield apparatus 1 of the prior art, a subtle magnetic field generated from a sample provided in an internal measurement space 7 is measured by a precise magnetic sensor (not shown). However, when a strong magnetic field is applied inside the shield apparatus 1 in order to excite the sample, in the shield apparatus 1 of the prior art, an eddy current is generated at the high-conductivity metal layer of the shield room 2, or the soft magnetic layer is magnetized by an excitation magnetic field. The eddy current is generated in the shield room 2 since each of the layers configuring the shield room 2 is formed as an all-connected closed surface structure as shown in FIGS. 1 and 2. That is, if an induced magnetic field is generated at the shield wall, the eddy current flows along the closed circuit for an extended period of time, and thus there is a problem in that a subtle magnetic field of the sample provided in the measurement space cannot be measured precisely due to the strong magnetic field generated by the continuous eddy current.
In addition, when the shield room 2 configuring the shield apparatus 1 is magnetized by the excitation magnetic field, in the prior art, a plurality of coil units 6 is insertedly installed on the surface of the soft magnetic layer, which is an inner layer of the shield wall, and a method of demagnetizing the soft magnetic layer by applying current to the coil units 6 is used. FIG. 3 is a perspective view showing a shield apparatus including coil units 6 inserted inside a shield wall according to a prior art. However, such a method has a problem in that it is difficult to insert a plurality of coils inside the shield room in manufacturing the shield apparatus, and manufacturing cost thereof is increased. Furthermore, when the coil units 6 are inserted inside the shield walls as shown in FIG. 3, the induced magnetic field generated by applying current to the coil units 6 may not reach the corners of the shield room 2, and thus there is a limit in demagnetizing the front surface of the shield room 2.
Accordingly, in order to solve the problems of the shield apparatus of the prior art, required are a shield apparatus and a method thereof capable of reducing the eddy current generated by the excitation magnetic field generated in the measurement space of the shield apparatus and efficiently demagnetizing the magnetized shield room.